U.S. patent application number 10/995837 was filed with the patent office on 2006-05-25 for sensing alignment of multiple layers.
Invention is credited to Jun Gao, Carl E. Picciotto, William M. Tong, Wei Wu.
Application Number | 20060110069 10/995837 |
Document ID | / |
Family ID | 36460999 |
Filed Date | 2006-05-25 |
United States Patent
Application |
20060110069 |
Kind Code |
A1 |
Tong; William M. ; et
al. |
May 25, 2006 |
Sensing alignment of multiple layers
Abstract
Using an imaging system in relation to a plurality of material
layers in an initial alignment state is provided, a first of the
plurality of material layers at least partially obscuring a second
of the plurality of material layers in the initial alignment state.
The first material layer is moved from a first position
corresponding to the initial alignment state to a second position
out of a field of view of the imaging system, and a first image of
the second material layer is stored. The first material layer is
moved back the first position to restore the initial alignment
state. A second image of the first material layer is acquired. The
second image and the stored first image are processed to determine
the initial alignment state.
Inventors: |
Tong; William M.; (San
Francisco, CA) ; Wu; Wei; (Mountain View, CA)
; Gao; Jun; (Saratoga, CA) ; Picciotto; Carl
E.; (Menlo Park, CA) |
Correspondence
Address: |
HEWLETT PACKARD COMPANY
P O BOX 272400, 3404 E. HARMONY ROAD
INTELLECTUAL PROPERTY ADMINISTRATION
FORT COLLINS
CO
80527-2400
US
|
Family ID: |
36460999 |
Appl. No.: |
10/995837 |
Filed: |
November 23, 2004 |
Current U.S.
Class: |
382/294 ;
382/291; 382/293 |
Current CPC
Class: |
G06T 7/0004
20130101 |
Class at
Publication: |
382/294 ;
382/291; 382/293 |
International
Class: |
G06K 9/32 20060101
G06K009/32; G06K 9/36 20060101 G06K009/36 |
Claims
1. A method for using an imaging system in relation to a plurality
of material layers in an initial alignment state, a first of said
plurality of material layers at least partially obscuring a second
of said plurality of material layers in the initial alignment
state, comprising: moving said first material layer from a first
position corresponding to said initial alignment state to a second
position out of a field of view of the imaging system; storing a
first image including at least a portion of said second material
layer having a second-layer alignment marker thereon; moving said
first material layer back to said first position to restore said
initial alignment state; and acquiring a second image including at
least a portion of said first material layer having a first-layer
alignment marker thereon; and processing said second image and said
stored first image to determine said initial alignment state
according to positions of said first-layer and second-layer
alignment markers.
2. The method of claim 1, further comprising moving said first
material layer to a third position corresponding to a desired
second alignment state between said first and second material
layers.
3. The method of claim 2, further comprising: acquiring a third
image including said portion of said first material layer having
said first-layer alignment marker thereon; and processing said
third image and said stored first image to verify said desired
second alignment state.
4. The method of claim 1, said first and second material layers
being separated by a distance greater than a depth of field of the
imaging system, further comprising: prior to said storing the first
image, causing a focal plane of the imaging system to correspond to
said second material layer; and prior to said acquiring the second
image, causing said focal plane to correspond to said first
material layer.
5. The method of claim 1, wherein said first material layer is
positioned below said second material layer relative to the imaging
system.
6. The method of claim 1, wherein said first material layer is
positioned above said second material layer relative to the imaging
system.
7. The method of claim 6, wherein said first material layer is
substantially opaque relative to the imaging system, wherein
relevant surface patterns of said first material layer are
positioned on an underside thereof relative to the imaging system,
and wherein said first-layer alignment marker comprises a
through-hole extending from said underside to a top side of said
first material layer.
8. The method of claim 1, said second material layer at least
partially obscuring said first material layer in the initial
alignment state, further comprising: prior to said acquiring the
second image, moving said second material layer from a third
position corresponding to said initial alignment state to a fourth
position out of the field of view of the imaging system; subsequent
to said acquiring the second image, storing the second image and
using said stored second image as said second image in said
processing; and moving said second material layer back to said
third position to restore said initial alignment state.
9. An apparatus for facilitating positioning of a plurality of
substantially parallel layers having an initial alignment state,
comprising: an imaging system having an optical axis extending
through said layers, a first of said layers at least partially
obscuring a second of said layers with respect to said imaging
system when in said initial alignment state; a positioning system
displacing said first layer from a first position corresponding to
said initial alignment state to a second position out of a field of
view of the imaging system, said first layer being maintained out
of said field of view as a first image is being acquired by said
imaging system including at least a portion of said second material
layer having a second-layer alignment marker thereon, said
positioning system subsequently moving said first layer back to
said first position to restore the initial alignment state; a
memory storing said first image; and a processor retrieving said
first image from said memory and receiving a second image acquired
by said imaging system, the second image including at least a
portion of said first layer having a first-layer alignment marker
thereon, said processor processing said second image and said
stored first image to determine said initial alignment state
according to positions of said first-layer and second-layer
alignment markers.
10. The apparatus of claim 9 wherein, subsequent to said processing
by said processor, said positioning system moves said first layer
to a third position corresponding to a desired second alignment
state between said first and second material layers.
11. The apparatus of claim 10, wherein, subsequent to said moving
of said first layer to said third position, said imaging system
acquires a third image including said portion of said first layer
having said first-layer alignment marker thereon, and said
processor processes said third image and said stored first image to
verify said desired second alignment state.
12. The apparatus of claim 9, said first and second layers being
separated by a distance greater than a depth of field of the
imaging system wherein, prior to the storing of the first image by
said memory, correspondence is caused between a focal plane of the
imaging system and said second layer, and prior to the acquisition
of the second image by said imaging system, correspondence is
caused between the focal plane of the imaging system and said first
material layer.
13. The apparatus of claim 9, wherein said first layer is
positioned below said second material layer relative to the imaging
system.
14. The apparatus of claim 9, wherein said first layer is
positioned above said second material layer relative to the imaging
system.
15. The apparatus of claim 14, wherein said first layer is
substantially opaque relative to the imaging system, wherein
relevant surface patterns of said first layer are positioned on an
underside thereof relative to the imaging system, and wherein said
first-layer alignment marker comprises a through-hole extending
from said underside to a top side of said first layer.
16. The apparatus of claim 9, said second material layer at least
partially obscuring said first material layer in the initial
alignment state, wherein: prior to the acquiring of the second
image by the imaging system, the positioning system moves the
second layer from a third position corresponding to said initial
alignment state to a fourth position out of the field of view of
the imaging system; subsequent to the acquisition of the second
image by the imaging system, said memory stores said second image,
and said processor uses said stored second image as the second
image in said processing; and wherein said positioning system moves
said second material layer back to said third position to restore
said initial alignment state.
17. A method for using an imaging system in relation to a plurality
of material layers in an initial alignment state, a first of said
plurality of material layers having substantially identical surface
features as a second of said plurality of material layers, the
first material layer at least partially obscuring the second
material layer in the initial alignment state, comprising: moving
said first material layer from a first position corresponding to
said initial alignment state to a second position out of a field of
view of the imaging system; storing a first image including at
least a portion of said second material layer; moving said first
material layer back to said first position to restore said initial
alignment state; acquiring a second image including at least a
portion of said first material layer; and processing said second
image and said stored first image to determine an initial relative
offset between said first and second material layers in said
initial alignment state according to an image displacement sensing
algorithm.
18. The method of claim 17, wherein said processing comprises:
cross-correlating said stored first image and said second image to
produce a cross-correlation function; and locating a global
extremum of said cross-correlation function.
19. The method of claim 18, said stored first image and said second
image comprising pixels, wherein said cross-correlating comprises
estimating a continuous correlation surface at sub-pixel locations,
said estimating comprising: computing a comparison function
comprising, for each of a predetermined number of relative offset
locations between the stored first image and the second image, a
comparison metric therebetween; and minimizing a cost function
between the comparison function and an estimated continuous
correlation surface, wherein the estimated continuous correlation
surface comprises a finite-element fitting function.
20. The method of claim 19, wherein said comparison metric
comprises a pixelwise sum of squared differences between said
stored first image and said second image at each offset, and
wherein said predetermined number of relative offsets is a
relatively small percentage of a total number of elements in said
stored first image.
21. The method of claim 17, wherein said processing comprises
determining a phase difference between frequency domain
representations of said first and second images.
22. The method of claim 17, further comprising moving said first
layer to a third position corresponding to a desired relative
offset between said first and second material layers.
23. The method of claim 22, further comprising: acquiring a third
image including said portion of said first material layer; and
processing said third image and said stored first image to verify
said desired relative offset.
24. The method of claim 17, said first and second material layers
being separated by a distance greater than a depth of field of the
imaging system, further comprising: prior to said storing the first
image, causing a focal plane of the imaging system to correspond to
said second material layer; and prior to said acquiring the second
image, causing said focal plane to correspond to said first
material layer.
25. The method of claim 17, wherein said first material layer is
positioned below said second material layer relative to the imaging
system.
26. The method of claim 17, wherein said first material layer is
positioned above said second material layer relative to the imaging
system.
27. The method of claim 17, said second material layer at least
partially obscuring said first material layer in the initial
alignment state, further comprising: prior to said acquiring the
second image, moving said second material layer from a third
position corresponding to said initial alignment state to a fourth
position out of the field of view of the imaging system; subsequent
to said acquiring the second image, storing the second image and
using said stored second image as said second image in said
processing; and moving said second material layer back to said
third position to restore said initial alignment state.
28. An apparatus for facilitating positioning of a plurality of
substantially identical parallel layers having an initial alignment
state, comprising: an imaging system having an optical axis
extending through said layers, a first of said layers at least
partially obscuring a second of said layers with respect to said
imaging system when in said initial alignment state; a positioning
system displacing said first layer from a first position
corresponding to said initial alignment state to a second position
out of a field of view of the imaging system, said first layer
being maintained out of said field of view as a first image is
being acquired by said imaging system including at least a portion
of said second material layer, said positioning system subsequently
moving said first layer back to said first position to restore the
initial alignment state; a memory storing said first image; and a
processor retrieving said first image from said memory and
receiving a second image acquired by said imaging system, the
second image including at least a portion of said first layer, said
processor processing said second image and said stored first image
to determine an initial relative offset between said first and
second layers in said initial alignment state according to an image
displacement sensing algorithm.
29. The apparatus of claim 28, wherein said image displacement
sensing algorithm comprises at least one of a differential image
flow algorithm, a tensor-based image flow algorithm, a
correlation-based image flow algorithm, a phase-shift-based image
flow algorithm, and an error analysis-based algorithm, each adapted
for rigid-body flow.
30. The apparatus of claim 29, said second material layer at least
partially obscuring said first material layer in the initial
alignment state, wherein: prior to the acquiring of the second
image by the imaging system, the positioning system moves the
second layer from a third position corresponding to said initial
alignment state to a fourth position out of the field of view of
the imaging system; subsequent to the acquisition of the second
image by the imaging system, said memory stores said second image,
and said processor uses said stored second image as the second
image in said processing; and wherein said positioning system moves
said second material layer back to said third position to restore
said initial alignment state.
31. A method for using an imaging system to determine a relative
position shift between a first layer and a second layer caused by a
repositioning of said layers from an initial configuration to a
subsequent configuration relative to the imaging system, said
layers being separated by a distance greater than a depth of field
of the imaging system in each of said initial and subsequent
configurations, comprising: with the imaging system focused on the
first layer in said initial configuration, acquiring a first image
of at least a portion of the first layer, and storing said first
image; with the imaging system focused on the second layer in said
initial configuration, acquiring a second image of at least a
portion of the second layer, and storing said second image; with
the imaging system focused on the first layer in said subsequent
configuration, acquiring a third image of said portion of the first
layer, and storing said third image; with the imaging system
focused on the second layer in said subsequent configuration,
acquiring a fourth image of said portion of the second layer;
processing said first and third images to determine a first
position shift of said first layer between said initial and
subsequent configurations; processing said second and fourth images
to determine a second position shift of said second layer between
said initial and subsequent configurations; and determining said
relative position shift between said first and second layers
according to said first and second position shifts.
32. The method of claim 31, said first layer comprising a
first-layer alignment marker in the imaged portion thereof, wherein
said processing said first and third images comprises determining
an absolute position of the first-layer alignment marker relative
to the imaging system in each of said first and third images.
33. The method of claim 32, said second layer comprising a
second-layer alignment marker in the imaged portion thereof,
wherein said processing said second and fourth images comprises
determining an absolute position of the second-layer alignment
marker relative to the imaging system in each of said second and
fourth images.
34. The method of claim 31, wherein said processing said first and
third images comprises an image displacement sensing algorithm,
whereby said first position shift can be determined without
requiring an alignment marker to be present in the imaged portion
of the first layer.
35. The method of claim 34, wherein said processing said first and
third images comprises: cross-correlating said first and third
images to produce a cross-correlation function; and locating a
global extremum of said cross-correlation function.
36. The method of claim 35, said first and third images comprising
pixels, wherein said cross-correlating comprises estimating a
continuous correlation surface at sub-pixel locations, said
estimating comprising: computing a comparison function comprising,
for each of a predetermined number of relative offset locations
between the first image and the third image, a comparison metric
therebetween; and minimizing a cost function between the comparison
function and an estimated continuous correlation surface, wherein
the estimated continuous correlation surface comprises a
finite-element fitting function.
37. The method of claim 36, wherein said comparison metric
comprises a pixelwise sum of squared differences between said
stored first image and said second image at each offset, and
wherein said predetermined number of relative offsets is a
relatively small percentage of a total number of elements in said
stored first image.
38. The method of claim 34, wherein said processing said first and
third images comprises determining a phase difference between
frequency domain representations of said first and second
images.
39. The method of claim 34, wherein said processing said second and
fourth images comprises an image displacement sensing
algorithm.
40. The method of claim 31, said first layer comprising a
first-layer alignment marker in the imaged portion thereof, wherein
said processing said first and third images comprises determining
an absolute position of the first-layer alignment marker relative
to the imaging system in each of said first and third images, and
wherein said processing said second and fourth images comprises an
image displacement sensing algorithm
41. The method of claim 31, the first layer at least partially
obscuring the second layer in the initial configuration, further
comprising, prior to said acquiring the second image, moving the
first layer from a first position corresponding to said initial
configuration to a second position out of a field of view of the
imaging system.
42. The method of claim 41, the second layer at least partially
obscuring the first layer in the initial configuration, further
comprising, prior to said acquiring the first image, moving the
second layer from a third position corresponding to said initial
configuration to a fourth position out of the field of view of the
imaging system.
43. The method of claim 42, said first and second layers at least
partially obscuring each other in the subsequent configuration,
further comprising: prior to said acquiring the third image, moving
the second layer from a fifth position corresponding to said
subsequent configuration to a sixth position out of the field of
view of the imaging system; after said acquiring the third image,
restoring the second layer to said fifth position; and prior to
said acquiring the fourth image, moving the first layer from a
seventh position corresponding to said subsequent configuration to
an eighth position out of the field of view of the imaging
system.
44. The method of claim 31, further comprising moving at least one
of said first and second layers toward a desired relative position
therebetween based on said determined relative position shift.
45. The method of claim 44, wherein said second layer is positioned
above said first layer relative to the imaging system in each of
said initial and subsequent configurations.
46. The method of claim 31, wherein said first layer is positioned
above said second layer relative to the imaging system in each of
said initial and subsequent configurations.
47. The method of claim 31, wherein said second layer is positioned
above said first layer relative to the imaging system in each of
said initial and subsequent configurations.
48. The method of claim 31, wherein at least one of said first and
second layers in said subsequent configuration comprises a
substituted but substantially identical version of said first or
second layer, respectively, in said initial configuration.
49. An apparatus for determining a relative position shift between
a first layer and a second layer caused by a repositioning of said
layers from an initial configuration to a subsequent configuration,
comprising: an imaging system having an optical axis extending
through said layers, said layers being separated by a distance
greater than a depth of field of the imaging system in each of said
initial and subsequent configurations; a memory storing a first
image of at least a portion of the first layer acquired with the
imaging system focused on the first layer in said initial
configuration, the memory further storing a second image of at
least a portion of the second layer acquired with the imaging
system focused on the second layer in said initial configuration,
the memory further storing a third image of said portion of the
first layer acquired with the imaging system focused on the first
layer in said subsequent configuration, the imaging system
acquiring a fourth image of said portion of the second layer when
focused thereon in said subsequent configuration; and a processor
processing said first and third images to determine a first
position shift of said first layer between said initial and
subsequent configurations, the processor further processing said
second and fourth images to determine a second position shift of
said second layer between said initial and subsequent
configurations, said processor determining said relative position
shift between said first and second layers according to said first
and second position shifts.
50. The apparatus of claim 49, said first layer comprising a
first-layer alignment marker in the imaged portion thereof, wherein
said processor processes said first and third images to determine
an absolute position of the first-layer alignment marker relative
to the imaging system in each of said first and third images.
51. The apparatus of claim 50, said second layer comprising a
second-layer alignment marker in the imaged portion thereof,
wherein said processor processes said second and fourth images to
determining an absolute position of the second-layer alignment
marker relative to the imaging system in each of said second and
fourth images.
52. The apparatus of claim 49, wherein said processor processes
said first and third images according to an image displacement
sensing algorithm, whereby said first position shift can be
determined without requiring an alignment marker to be present in
the imaged portion of the first layer.
53. The apparatus of claim 52, wherein said image displacement
sensing algorithm comprises at least one of a differential image
flow algorithm, a tensor-based image flow algorithm, a
correlation-based image flow algorithm, a phase-shift-based image
flow algorithm, and an error analysis-based algorithm, each adapted
for rigid-body flow.
54. The apparatus of claim 53, wherein said processor processes
said second and fourth images according to an image displacement
sensing algorithm.
55. The apparatus of claim 49, said first layer comprising a
first-layer alignment marker in the imaged portion thereof, wherein
said processor processes said first and third images to determine
an absolute position of the first-layer alignment marker relative
to the imaging system in each of said first and third images, and
wherein said processor processes said second and fourth images
according to an image displacement sensing algorithm.
56. The apparatus of claim 49, wherein at least one of said first
and second layers in said subsequent configuration comprises a
substituted but substantially identical version of said first or
second layer, respectively, in said initial configuration.
57. The apparatus of claim 49, said first layer at least partially
obscuring said second layer in the initial configuration, said
apparatus further comprising a positioning system, wherein prior to
the acquisition of the second image by the imaging system, the
positioning system moves the first layer from a first position
corresponding to said initial configuration to a second position
out of a field of view of the imaging system.
58. The apparatus of claim 57, the second layer at least partially
obscuring the first layer in the initial configuration, wherein
prior to the acquisition of the first image by the imaging system,
the positioning system moves the second layer from a third position
corresponding to said initial configuration to a fourth position
out of the field of view of the imaging system.
59. The apparatus of claim 58, said first and second layers at
least partially obscuring each other in the subsequent
configuration, wherein: prior to the acquisition of the third image
by the imaging system, the positioning system moves the second
layer from a fifth position corresponding to said subsequent
configuration to a sixth position out of the field of view of the
imaging system; after the acquisition of the third image by the
imaging system, the positioning system restores the second layer to
said fifth position; and prior to the acquisition of the fourth
image, the positioning system moves the first layer from a seventh
position corresponding to said subsequent configuration to an
eighth position out of the field of view of the imaging system.
60. The apparatus of claim 49 wherein said positioning system moves
at least one of said first and second layers toward a desired
relative position therebetween based on said determined relative
position shift.
61. The apparatus of claim 49, wherein said first layer is
positioned above said second layer relative to the imaging system
in each of said initial and subsequent configurations.
62. The apparatus of claim 49, wherein said second layer is
positioned above said first layer relative to the imaging system in
each of said initial and subsequent configurations.
63. A method for using an imaging system in relation to a plurality
of material layers, a first of said plurality of material layers
having substantially identical surface features as a second of said
plurality of material layers, said first and second material layers
being separated by a distance greater than a depth of field of the
imaging system, comprising: causing a focal plane of the imaging
system to correspond to said first material layer; storing a first
image including at least a portion of said first material layer;
causing said focal plane to correspond to said second material
layer acquiring a second image including at least a portion of said
second material layer; and processing said second image and said
stored first image to determine a position of said second material
layer relative to said first material layer according to an image
displacement sensing algorithm.
64. The method of claim 63, wherein said processing comprises:
cross-correlating said stored first image and said second image to
produce a cross-correlation function; and locating a global
extremum of said cross-correlation function.
65. The method of claim 64, said stored first image and said second
image comprising pixels, wherein said cross-correlating comprises
estimating a continuous correlation surface at sub-pixel locations,
said estimating comprising: computing a comparison function
comprising, for each of a predetermined number of relative offset
locations between the stored first image and the second image, a
comparison metric therebetween; and minimizing a cost function
between the comparison function and an estimated continuous
correlation surface, wherein the estimated continuous correlation
surface comprises a finite-element fitting function.
66. The method of claim 65, wherein said comparison metric
comprises a pixelwise sum of squared differences between said
stored first image and said second image at each offset, and
wherein said predetermined number of relative offsets is a
relatively small percentage of a total number of elements in said
stored first image.
67. The method of claim 63, wherein said processing comprises
determining a phase difference between frequency domain
representations of said first and second images.
68. The method of claim 63, further comprising moving said second
layer to a desired position relative to said first layer.
69. An apparatus for position sensing in relation to a plurality of
substantially identical parallel layers, comprising: an imaging
system having an optical axis extending through said layers, said
imaging system having a depth of field less than a separation
distance between a first of said layers and a second of said
layers, said imaging system acquiring a first image including at
least a portion of said first layer while focused on said first
layer; a memory storing said first image; and a processor
retrieving said first image from said memory and receiving a second
image acquired by said imaging system while focused on said second
layer, the second image including at least a portion of said second
layer, said processor processing said second image and said stored
first image according to an image displacement sensing algorithm to
determine a relative offset between said first and second
layers.
70. The apparatus of claim 69, further comprising a positioning
system moving said second layer to a desired offset relative to
said first layer.
71. The apparatus of claim 69, wherein said image displacement
sensing algorithm comprises at least one of a differential image
flow algorithm, a tensor-based image flow algorithm, a
correlation-based image flow algorithm, a phase-shift-based image
flow algorithm, and an error analysis-based algorithm, each adapted
for rigid-body flow.
72. A method for using an imaging system to determine a relative
position shift between a first layer and a second layer caused by a
repositioning of said layers from an initial configuration to a
subsequent configuration relative to the imaging system, the first
layer at least partially obscuring the second layer in the initial
configuration, comprising: with the first and second layers in said
initial configuration, acquiring a first image of at least a
portion of the first layer, and storing said first image; moving
the first layer from a first position corresponding to said initial
configuration to a second position out of a field of view of the
imaging system, acquiring a second image of at least a portion of
the second layer, and storing said second image; with the first and
second layers in said subsequent configuration, acquiring a third
image of said portion of the first layer, storing said third image,
and acquiring a fourth image of said portion of the second layer;
processing said first and third images to determine a first
position shift of said first layer between said initial and
subsequent configurations; processing said second and fourth images
to determine a second position shift of said second layer between
said initial and subsequent configurations; and determining said
relative position shift between said first and second layers
according to said first and second position shifts.
73. The method of claim 72, said first layer comprising a
first-layer alignment marker in the imaged portion thereof, wherein
said processing said first and third images comprises determining
an absolute position of the first-layer alignment marker relative
to the imaging system in each of said first and third images.
74. The method of claim 73, said second layer comprising a
second-layer alignment marker in the imaged portion thereof,
wherein said processing said second and fourth images comprises
determining an absolute position of the second-layer alignment
marker relative to the imaging system in each of said second and
fourth images.
75. The method of claim 72, wherein said processing said first and
third images comprises an image displacement sensing algorithm,
whereby said first position shift can be determined without
requiring an alignment marker to be present in the imaged portion
of the first layer.
76. The method of claim 75, wherein said processing said first and
third images comprises: cross-correlating said first and third
images to produce a cross-correlation function; and locating a
global extremum of said cross-correlation function.
77. The method of claim 76, said first and third images comprising
pixels, wherein said cross-correlating comprises estimating a
continuous correlation surface at sub-pixel locations, said
estimating comprising: computing a comparison function comprising,
for each of a predetermined number of relative offset locations
between the first image and the third image, a comparison metric
therebetween; and minimizing a cost function between the comparison
function and an estimated continuous correlation surface, wherein
the estimated continuous correlation surface comprises a
finite-element fitting function.
78. The method of claim 77, wherein said comparison metric
comprises a pixelwise sum of squared differences between said
stored first image and said second image at each offset, and
wherein said predetermined number of relative offsets is a
relatively small percentage of a total number of elements in said
stored first image.
79. The method of claim 75, wherein said processing said first and
third images comprises determining a phase difference between
frequency domain representations of said first and second
images.
80. The method of claim 75, wherein said processing said second and
fourth images comprises an image displacement sensing
algorithm.
81. The method of claim 72, said first layer comprising a
first-layer alignment marker in the imaged portion thereof, wherein
said processing said first and third images comprises determining
an absolute position of the first-layer alignment marker relative
to the imaging system in each of said first and third images, and
wherein said processing said second and fourth images comprises an
image displacement sensing algorithm.
82. The method of claim 72, the second layer at least partially
obscuring the first layer in the initial configuration, further
comprising, prior to said acquiring the first image, moving the
second layer from a third position corresponding to said initial
configuration to a fourth position out of the field of view of the
imaging system.
83. The method of claim 82, said first and second layers at least
partially obscuring each other in the subsequent configuration,
further comprising: prior to said acquiring the third image, moving
the second layer from a fifth position corresponding to said
subsequent configuration to a sixth position out of the field of
view of the imaging system; after said acquiring the third image,
restoring the second layer to said fifth position; and prior to
said acquiring the fourth image, moving the first layer from a
seventh position corresponding to said subsequent configuration to
an eighth position out of the field of view of the imaging
system.
84. The method of claim 72, further comprising moving at least one
of said first and second layers toward a desired relative position
therebetween based on said determined relative position shift.
85. The method of claim 72, wherein said first layer is positioned
above said second layer relative to the imaging system in each of
said initial and subsequent configurations.
86. The method of claim 72, wherein said second layer is positioned
above said first layer relative to the imaging system in each of
said initial and subsequent configurations.
87. The method of claim 72, wherein at least one of said first and
second layers in said subsequent configuration comprises a
substituted but substantially identical version of said first or
second layer, respectively, in said initial configuration.
88. An apparatus for determining a relative position shift between
a first layer and a second layer caused by a repositioning of said
layers from an initial configuration to a subsequent configuration,
the first layer at least partially obscuring the second layer in
the initial configuration, comprising: an imaging system having an
optical axis extending through said first and second layers, the
imaging system acquiring a first image including at least a portion
of the first layer in said initial configuration; a positioning
system displacing said first layer from a first position
corresponding to said initial configuration to a second position
out of a field of view of the imaging system, said first layer
being maintained out of said field of view as a second image is
being acquired by said imaging system including at least a portion
of said second material layer, said positioning system subsequently
moving said first layer back to said first position to restore the
initial configuration; a memory storing said first and second
images, the memory further storing a third image of said portion of
the first layer acquired by the imaging system in said subsequent
configuration, the imaging system acquiring a fourth image of said
portion of the second layer in said subsequent configuration; a
processor processing said first and third images to determine a
first position shift of said first layer between said initial and
subsequent configurations, the processor further processing said
second and fourth images to determine a second position shift of
said second layer between said initial and subsequent
configurations, said processor determining said relative position
shift between said first and second layers according to said first
and second position shifts.
89. The apparatus of claim 88, said first layer comprising a
first-layer alignment marker in the imaged portion thereof, wherein
said processor processes said first and third images to determine
an absolute position of the first-layer alignment marker relative
to the imaging system in each of said first and third images.
90. The apparatus of claim 89, said second layer comprising a
second-layer alignment marker in the imaged portion thereof,
wherein said processor processes said second and fourth images to
determining an absolute position of the second-layer alignment
marker relative to the imaging system in each of said second and
fourth images.
91. The apparatus of claim 88, wherein said processor processes
said first and third images according to an image displacement
sensing algorithm, whereby said first position shift can be
determined without requiring an alignment marker to be present in
the imaged portion of the first layer.
92. The apparatus of claim 91, wherein said image displacement
sensing algorithm comprises at least one of a differential image
flow algorithm, a tensor-based image flow algorithm, a
correlation-based image flow algorithm, a phase-shift-based image
flow algorithm, and an error analysis-based algorithm, each adapted
for rigid-body flow.
93. The apparatus of claim 92, wherein said processor processes
said second and fourth images according to an image displacement
sensing algorithm.
94. The apparatus of claim 88, said first layer comprising a
first-layer alignment marker in the imaged portion thereof, wherein
said processor processes said first and third images to determine
an absolute position of the first-layer alignment marker relative
to the imaging system in each of said first and third images, and
wherein said processor processes said second and fourth images
according to an image displacement sensing algorithm.
95. The apparatus of claim 88, wherein at least one of said first
and second layers in said subsequent configuration comprises a
substituted but substantially identical version of said first or
second layer, respectively, in said initial configuration.
96. The apparatus of claim 88, the second layer at least partially
obscuring the first layer in the initial configuration, wherein
prior to the acquisition of the first image by the imaging system,
the positioning system moves the second layer from a third position
corresponding to said initial configuration to a fourth position
out of the field of view of the imaging system.
97. The apparatus of claim 96, said first and second layers at
least partially obscuring each other in the subsequent alignment,
wherein: prior to the acquisition of the third image by the imaging
system, the positioning system moves the second layer from a fifth
position corresponding to said subsequent configuration to a sixth
position out of the field of view of the imaging system; after the
acquisition of the third image by the imaging system, the
positioning system restores the second layer to said fifth
position; and prior to the acquisition of the fourth image, the
positioning system moves the first layer from a seventh position
corresponding to said subsequent configuration to an eighth
position out of the field of view of the imaging system.
98. The apparatus of claim 88 wherein said positioning system moves
at least one of said first and second layers toward a desired
relative position therebetween based on said determined relative
position shift.
99. The apparatus of claim 88, wherein said second layer is
positioned above said first layer relative to the imaging system in
each of said initial and subsequent configurations.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The subject matter of this patent specification relates at
least in part to the subject matter of U.S. Ser. No. ______
(Attorney Docket No. 200404823) filed even date herewith, and which
is incorporated by reference herein.
FIELD
[0002] This patent specification relates to sensing and/or
controlling at least one of an alignment state and a relative
position shift among multiple material layers using an imaging
system.
BACKGROUND
[0003] The generation of small devices often involves an alignment
of multiple material layers, e.g., two or more material layers,
with the assistance of an imaging system. For example, in one
scenario, the material layers are positioned substantially parallel
to each other and are spaced apart by an amount that is relatively
small compared to their overall dimensions. An imaging system
having an optical axis perpendicular to the material layers is used
to image one or more alignment markers on or within each layer.
Relative position is established according to alignment marker
positions. Alignment markers can comprise markers provided
explicitly for alignment purposes, or can comprise known landmarks
identified among features present on the material layer.
[0004] One issue can arise in the context of material layers that
can obscure other material layers relative to the imaging system.
As used herein, a first layer obscures a second layer if a clean
image of the second layer cannot be obtained by the imaging system
in the presence of the first layer. Depending on the selection of
algorithm used for alignment sensing or control, the presence of
obscuring material layers may confound performance in the alignment
sensing and/or control process. Notably, a first layer may obscure
a second layer even if the first layer is positioned below the
second layer relative to the imaging system. For example, features
or textures of a lower layer may show through an upper layer such
that a clean image of upper layer cannot be obtained in the
presence of the lower layer.
[0005] Other issues that can arise, either alone or in combination
with obscuring material layers, relate to the ever-shrinking nature
of devices and the ever-changing nature of their fabrication
processes. One issue brought about by shrinking feature sizes is
that the spacing between material layers may begin to exceed the
depth of field of the imaging system used in the alignment process.
Another issue is that it may not always be desirable or practical
to use alignment markers for sensing device alignment and/or for
sensing relative position shifts. At the same time, however, the
need for exacting alignment tolerances remains. By way of example,
it may be desirable to measure very small changes in an alignment
state between layers even where no alignment markers are
present.
SUMMARY
[0006] In accordance with an embodiment, a method for using an
imaging system in relation to a plurality of material layers in an
initial alignment state is provided, a first of the plurality of
material layers at least partially obscuring a second of the
plurality of material layers in the initial alignment state. The
first material layer is moved from a first position corresponding
to the initial alignment state to a second position out of a field
of view of the imaging system, and a first image including at least
a portion of the second material layer having a second-layer
alignment marker thereon is stored. The first material layer is
moved back to the first position to restore the initial alignment
state. A second image including at least a portion of the first
material layer having a first-layer alignment marker thereon is
acquired. The second image and the stored first image are processed
to determine the initial alignment state according to positions of
the first-layer and second-layer alignment markers.
[0007] Also provided is a an apparatus for facilitating positioning
of a plurality of substantially parallel layers having an initial
alignment state. The apparatus comprises an imaging system having
an optical axis extending through the layers, a first of the layers
at least partially obscuring a second of the layers with respect to
the imaging system when in the initial alignment state. The
apparatus further comprises a positioning system displacing the
first layer from a first position corresponding to the initial
alignment state to a second position out of a field of view of the
imaging system, the first layer being maintained out of the field
of view as a first image is being acquired by the imaging system
including at least a portion of the second material layer having a
second-layer alignment marker thereon. The positioning system
subsequently moves the first layer back to the first position to
restore the initial alignment state. The apparatus further
comprises a memory storing the first image. The apparatus further
comprises a processor retrieving the first image from the memory
and receiving a second image acquired by the imaging system, the
second image including at least a portion of the first layer having
a first-layer alignment marker thereon. The processor processes the
second image and the stored first image to determine the initial
alignment state according to positions of the first-layer and
second-layer alignment markers.
[0008] Also provided is a method for using an imaging system in
relation to a plurality of material layers in an initial alignment
state, a first of the plurality of material layers having
substantially identical surface features as a second of the
plurality of material layers, the first material layer at least
partially obscuring the second material layer in the initial
alignment state. The first material layer is moved from a first
position corresponding to the initial alignment state to a second
position out of a field of view of the imaging system. A first
image including at least a portion of the second material layer is
stored. The first material layer is moved back to the first
position to restore the initial alignment state. A second image is
acquired including at least a portion of the first material layer.
The second image and the stored first image are processed to
determine an initial relative offset between the first and second
material layers in the initial alignment state according to an
image displacement sensing algorithm.
[0009] Also provided is an apparatus for facilitating positioning
of a plurality of substantially identical parallel layers having an
initial alignment state. The apparatus comprises an imaging system
having an optical axis extending through the layers, a first of the
layers at least partially obscuring a second of the layers with
respect to the imaging system when in the initial alignment state.
The apparatus further comprises a positioning system displacing the
first layer from a first position corresponding to the initial
alignment state to a second position out of a field of view of the
imaging system. The first layer is maintained out of the field of
view as a first image is being acquired by the imaging system
including at least a portion of the second material layer. The
positioning system subsequently moves the first layer back to the
first position to restore the initial alignment state. The
apparatus further comprises a memory storing the first image. The
apparatus further comprises a processor retrieving the first image
from the memory and receiving a second image acquired by the
imaging system, the second image including at least a portion of
the first layer. The processor processes the second image and the
stored first image to determine an initial relative offset between
the first and second layers in the initial alignment state
according to an image displacement sensing algorithm.
[0010] Also provided is a method for using an imaging system to
determine a relative position shift between a first layer and a
second layer caused by a repositioning of the layers from an
initial configuration to a subsequent configuration relative to the
imaging system. The layers are separated by a distance greater than
a depth of field of the imaging system in each of the initial and
subsequent configurations. With the imaging system focused on the
first layer in the initial configuration, a first image of at least
a portion of the first layer is acquired and stored. With the
imaging system focused on the second layer in the initial
configuration, a second image of at least a portion of the second
layer is acquired and stored. With the imaging system focused on
the first layer in the subsequent configuration, a third image of
the portion of the first layer is acquired and stored. With the
imaging system focused on the second layer in the subsequent
configuration, a fourth image of the portion of the second layer is
acquired. The first and third images are processed to determine a
first position shift of the first layer between the initial and
subsequent configurations. The second and fourth images are
processed to determine a second position shift of the second layer
between the initial and subsequent configurations, and the relative
position shift between the first and second layers is determined
according to the first and second position shifts.
[0011] Also provided is an apparatus for determining a relative
position shift between a first layer and a second layer caused by a
repositioning of the layers from an initial configuration to a
subsequent configuration. The apparatus comprises an imaging system
having an optical axis extending through the layers, the layers
being separated by a distance greater than a depth of field of the
imaging system in each of the initial and subsequent
configurations. The apparatus further comprises a memory storing a
first image of at least a portion of the first layer, the first
image acquired with the imaging system focused on the first layer
in the initial configuration. The memory further stores a second
image of at least a portion of the second layer, the second image
acquired with the imaging system focused on the second layer in the
initial configuration. The memory further stores a third image of
the portion of the first layer, the third image acquired with the
imaging system focused on the first layer in the subsequent
configuration. The imaging system acquires a fourth image of the
portion of the second layer when focused thereon in the subsequent
configuration. The apparatus further comprises a processor
processing the first and third images to determine a first position
shift of the first layer between the initial and subsequent
configurations. The processor also processes the second and fourth
images to determine a second position shift of the second layer
between the initial and subsequent configurations. The processor
determines the relative position shift between the first and second
layers according to the first and second position shifts.
[0012] Also provided is a method for using an imaging system in
relation to a plurality of material layers, a first of the
plurality of material layers having substantially identical surface
features as a second of the plurality of material layers, the first
and second material layers being separated by a distance greater
than a depth of field of the imaging system. A focal plane is
brought into correspondence with the first material layer and a
first image is stored including at least a portion of the first
material layer. The focal plane is brought into correspondence with
the second material layer and a second image is acquired including
at least a portion of the second material layer. The stored first
image and the second image are processed according to an image
displacement sensing algorithm to determine a position of the
second material layer relative to the first material layer.
[0013] Also provided is an apparatus position sensing in relation
to a plurality of substantially identical parallel layers. The
apparatus comprises an imaging system having an optical axis
extending through the layers, the imaging system having a depth of
field less than a separation distance between a first of the layers
and a second of the layers, the imaging system acquiring a first
image including at least a portion of said first layer while
focused on the first layer. The apparatus further comprises a
memory storing the first image. The apparatus further comprises a
processor retrieving the first image from the memory and receiving
a second image acquired by the imaging system while focused on the
second layer, the second image including at least a portion of the
second layer, the processor processing the second image and the
stored first image according to an image displacement sensing
algorithm to determine a relative offset between the first and
second layers.
[0014] Also provided is a method for using an imaging system to
determine a relative position shift between a first layer and a
second layer caused by a repositioning of the layers from an
initial configuration to a subsequent configuration relative to the
imaging system, the first layer at least partially obscuring the
second layer in the initial configuration. With the first and
second layers in the initial configuration, a first image of at
least a portion of the first layer is acquired and stored. The
first layer is moved from a first position corresponding to the
initial configuration to a second position out of a field of view
of the imaging system, and a second image of at least a portion of
the second layer is acquired and stored. With the first and second
layers in the subsequent configuration, a third image of the
portion of the first layer is acquired and stored, and a fourth
image of the portion of the second layer is acquired. The first and
third images are processed to determine a first position shift of
the first layer between the initial and subsequent configurations.
The second and fourth images are processed to determine a second
position shift of the second layer between the initial and
subsequent configurations. A relative position shift between the
first and second layers is then determined according to the first
and second position shifts.
[0015] Also provided is an apparatus for determining a relative
position shift between a first layer and a second layer caused by a
repositioning of the layers from an initial configuration to a
subsequent configuration, the first layer at least partially
obscuring the second layer in the initial configuration. The
apparatus comprises an imaging system having an optical axis
extending through the first and second layers, the imaging system
acquiring a first image including at least a portion of the first
layer in the initial configuration. The apparatus further comprises
a positioning system displacing the first layer from a first
position corresponding to the initial configuration to a second
position out of a field of view of the imaging system, the first
layer being maintained out of the field of view as a second image
is being acquired by the imaging system including at least a
portion of the second material layer, the positioning system
subsequently moving the first layer back to the first position to
restore the initial configuration. The apparatus further comprises
a memory storing the first and second images, the memory further
storing a third image of the portion of the first layer acquired by
the imaging system in the subsequent configuration, the imaging
system acquiring a fourth image of the portion of the second layer
in the subsequent configuration. The apparatus further comprises a
processor processing the first and third images to determine a
first position shift of the first layer between the initial and
subsequent configurations, the processor further processing the
second and fourth images to determine a second position shift of
the second layer between the initial and subsequent configurations,
the processor determining the relative position shift between the
first and second layers according to the first and second position
shifts.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 illustrates an apparatus for determining at least one
of an alignment state and a relative position shift between two
material layers according to an embodiment;
[0017] FIG. 2 illustrates an apparatus for determining at least one
of an alignment state and a relative position shift among three or
more material layers according to an embodiment;
[0018] FIGS. 3 and 4 illustrate examples of alignment markers in
different alignment states;
[0019] FIG. 5A illustrates examples of surface textures;
[0020] FIGS. 5B and 5C illustrate examples of moving a layer out of
a field of view of an imaging system;
[0021] FIGS. 6-11 illustrate determining alignment states according
to one or more embodiments;
[0022] FIGS. 12-16 illustrate determining relative layer position
shifts according to one or more embodiments;
[0023] FIG. 17 illustrates determining alignment states according
to an embodiment; and
[0024] FIG. 18 illustrates determining a relative layer position
shift according an embodiment.
DETAILED DESCRIPTION
[0025] FIG. 1 illustrates an apparatus 100 for determining at least
one of an alignment state and a relative position shift between two
layers 102 and 104 according to an embodiment. Apparatus 100
comprises an imaging system 106 having an optical axis 107
extending through the layers 102 and 104. Imaging system 106 is
fixed relative to a fixed reference frame 110. It is to be
appreciated, of course, that the fixed reference frame 110 may
itself be in motion, either in a start-stop sense or a continuous
sense, relative to another reference frame such as the floor, a
fabrication machine, etc.
[0026] In one embodiment, which is described by way of illustration
and not by way of limitation, layer 102 is a mold for use in a
nanoimprint lithography process. The nanoimprint lithography mold
may comprise, for example, a silicon wafer having a layer of
SiO.sub.2 for use in a hot embossing process, or may comprise a
quartz mold for use in an ultraviolet curing-based process. The
layer 104 is, for example, a resist-coated substrate. However, it
is to be appreciated that the scope of the present teachings is
applicable in a wide variety of other scenarios. In another
example, the layer 102 can be a mask and the layer 104 can be a
sample, respectively, in a proximity or contact lithography
system.
[0027] In one embodiment, the imaging system 106 comprises a
single-objective microscope with a high-NA (numerical aperture)
objective lens for achieving submicron resolution or better. The NA
can be in the range, for example, of 0.8 to 0.95 for air-immersed
samples. The imaging system 106 may have a depth of field of
perhaps 2-3 microns. Generally speaking, depth of field refers to a
distance range around the focal plane along the optical axis at
which imaging can be achieved within a desired lateral resolution.
In other embodiments, lower-NA objective lenses may be used having
larger field depths. In general, several embodiments herein are
advantageous where the depth of field of the imaging system 106 is
small compared to the spacing between the layers. Several other
embodiments herein are advantageous where the depth of field of the
imaging system 106 is comparable to, or greater than, to the
spacing between the layers. Illustrated in FIG. 1 is a field of
view 122 of the imaging system 106, along with portions 118 and
120, respectively, of the layers 102 and 104 that are within the
field of view 122. It is to be appreciated that, as used herein,
field of view can refer to a sub-area within a total area imaged by
the imaging system 106. Thus, for example, the field of view 760 of
FIG. 7, infra, may represent a smaller area within the field of
view 122 of FIG. 1.
[0028] Apparatus 100 further comprises a fine positioning system
108 capable of translating the layers 102 and 104 by desired
distances with fine tolerances at least comparable to the desired
tolerances for alignment sensing and/or control. More particularly,
if one of the layers 102 or 104, or portion thereof, is in a first
position P.sub.0 relative to the frame of reference 110 within the
field of view of the imaging system 106, the fine positioning
system 108 is capable of (i) moving that layer or portion thereof
out of the field of view, and then (ii) moving that layer or
portion thereof back to the first position P.sub.0 within a
tolerance .DELTA.P, where .DELTA.P is comparable to or finer than
the desired tolerances for alignment sensing and/or control. By way
of example and not by way of limitation, the desired tolerances,
and therefore the precision of the fine positioning system 108, may
range from the order of several micrometers for some applications
to the order of 1 nanometer, or even less, for other applications.
In one embodiment, fine positioning system 108 comprises
piezoelectric actuators and/or stepper motors geared and
controlled, usually with internal feedback control systems, to
achieve nanometer-level precision.
[0029] A general position control system 116 may be provided in
conjunction with the apparatus 100. The general position control
system 110 generally provides for more general, larger-scale
movements, such as for the complete insertion and withdrawal of the
layers 102 and 104 into and out of the apparatus 100. In one
embodiment, general position control system 116 comprises a human
hand or human-driven positioning tool. In other embodiments the
general position control system 116 can be realized by various
automated conveyors or other positioning systems associated with
micro-fabrication or nano-fabrication. Together, general position
control system 116 and the fine position control system 108 can
collectively provide the layer movement functionalities described
herein. Notably, the functionalities of the general position
control system 116 and the fine position control system 108 can be
provided by the same device or system. Apparatus 100 further
comprises a processor 112 having an associated memory 114 that
interacts with the imaging system 106, fine position control system
108, and/or general position control system 116 in accordance with
the functionalities described herein.
[0030] FIG. 2 illustrates an apparatus 200 for determining at least
one of an alignment state and a relative position shift among three
layers, comprising items 206-216 analogous to items 106-116 of FIG.
1, respectively, with the additional capability of accommodating a
third layer 224. In general, the functionalities described herein
are readily applicable to the case of three layers, as in FIG. 2,
or more layers without departing from the scope of the present
teachings. However, for purposes of clarity and not by way
limitation, embodiments relating to two material layers are
described further herein.
[0031] FIGS. 3 and 4 illustrate examples of layers 302, 304, and
306 having alignment markers thereon, as well as composite images
308 and 408 corresponding to hypothetical composite images formed
from merging the three layers in their current alignment state. As
used herein, alignment state refers to an alignment condition.
Thus, any vertical configuration of two or more layers possess an
alignment state, by virtue of their being in some type of relative
position. It is to be further appreciated that either image 308 or
image 408 may reflect a desired state of alignment for the material
layers 302-306, depending on the particular application, processes,
process history, or other circumstances.
[0032] In cases in which a first layer obscures an alignment marker
of a second layer, it has been found useful to obviate this
occlusion with the assistance of a fine positioning system. In
particular, the fine positioning system temporarily moves the first
layer to the side, an image is stored of the now un-obscured second
layer, the fine positioning system restores the first layer to its
original position, and then the clean stored image of the second
layer is used to determine alignment state instead of an obscured
image of the second layer. Depending on the segmentation algorithm
used to identify the alignment marker, this process can been useful
even in the event of minor occlusions, because some segmentation
and location algorithms might be highly sensitive to such
occlusions. These methods are readily applicable in the case of
K>2 layers as well, in which case layers 1, 2, . . . , i-1, i+1,
. . . , K are all temporarily moved to the side while an image of
the i.sup.th layer is acquired and stored. This method has also
been found particularly useful and efficient in contexts where the
layers are separated by a distance greater than a depth of field of
the imaging system, as multiple issues can be resolved with a
common set of stored images. Several embodiments herein are
advantageously applied in the context of layers having alignment
markers such as those of the material layers 302-306.
[0033] FIG. 5A illustrates examples of layers 502, 504, and 506
having surface textures. The layers 502-504 are devoid of any
alignment markers, whereas the "corner" feature in layer 506 may,
or may not, constitute an alignment marker depending on how unique
and/or identifiable it is. However, regardless of whether layer 506
represents an alignment marker, several other embodiments herein
are advantageously applied in sensing relative position shifts of
material layers between initial and subsequent configurations even
where alignment markers are not present, provided only that there
is some type of surface texture present.
[0034] In nanoimprint lithography environments, for example, it may
be desirable to place a first and second layer in an initial
alignment state not necessarily dictated by alignment markers,
while also (i) maintaining that initial alignment state, or (ii)
sensing changes in that initial alignment state, or (iii) altering
that alignment state as process requirements dictate, or (iv) doing
any other activity that may require sensing of relative position
shifts between the first and second layers. It has been found
beneficial to use image displacement sensing algorithms on a
layer-by-layer basis, comparing an image of each layer in the
subsequent configuration to an image of that same layer in the
initial configuration to determine a position shift vector, and
then performing vector subtraction on the position shift vectors
for different layers to determine the relative position shifts
between layers. Alignment marks are not needed in this embodiment,
although there should be enough surface texture on each layer to
allow operation of such image displacement sensing algorithms, and
although the surface texture of any particular layer should not be
obscured by other layers. The required surface texture can be
provided either by native material patterns or by applied surface
patterns, including alignment markers themselves. In the event a
first layer does obscure a surface texture of a second layer, it
has been found useful to obviate this occlusion using a fine
positioning system, by temporarily moving the first layer to the
side, store an image of the now un-obscured second layer, restoring
the first layer to its original position, and then processing the
clean stored version of the second layer according to the image
displacement sensing algorithm. These methods are readily
applicable in the case of K>2 layers as well, in which case
layers 1, 2, . . . , i-1, i+1, . . . , K are all temporarily moved
to the side while an image of the i.sup.th layer is acquired and
stored. These methods have also been found particularly useful and
efficient in contexts where the layers are separated by a distance
greater than a depth of field of the imaging system, as multiple
issues can be resolved with a common set of stored images.
[0035] Image displacement sensing algorithm refers to a class of
processing algorithms in which a first matrix M.sub.t(x,y) and a
second matrix M.sub.t+.DELTA.t(x,y) are processed to compute a
displacement vector .DELTA.M therebetween under a rigid body
assumption, i.e., under an assumption that features or textures of
the underlying item do not change over the interval .DELTA.t. In
one embodiment, image displacement sensing algorithm refers to a
subclass of image flow algorithms specially adapted for fast
computation under the rigid body assumption. In another embodiment,
image displacement sensing algorithm refers to a subclass of image
flow algorithms specially adapted for detection of rigid-body
displacements to sub-pixel resolutions. In still another
embodiment, image displacement sensing algorithm refers to a
subclass of image flow algorithms specially adapted to achieve both
fast computation and sub-pixel resolution under the rigid body
assumption.
[0036] In accordance with an embodiment, it has been found that one
particularly useful image displacement algorithm cross-correlates
the first and second matrices to produce a cross-correlation
function, and then locates a global extremum of the
cross-correlation function. Preferably, the cross-correlating
further comprises estimating a continuous correlation surface at
sub-pixel locations. A comparison function is computed comprising,
for a predetermined number N of relative offset locations (N=9, 25,
for example), a sum of squared differences, or other comparison
metric, between the elements of the first and second matrices. A
cost function is minimized between the comparison function and an
estimated continuous correlation surface, wherein the estimated
continuous correlation surface is a fitting function whose
parameters are varied to minimize the cost function. In one
embodiment, the fitting function is equivalent to a truncated
Taylor series, although the scope of the present teachings is not
so limited. In one embodiment in which the number of offset
locations N is 9, the fitting function has six parameters, although
the scope of the present teachings is not so limited. A global
extremum of the estimated continuous correlation surface is located
to determine the displacement, whereby the displacement can be
determined to a sub-pixel resolution. Discussions of comparable
methods used for optically-acquired images can be found in U.S.
Pat. No. 5,149,180 and U.S. Pat. No. 6,195,475. In accordance with
another embodiment, it has been found that another particularly
useful image displacement algorithm computes phase differences
between frequency domain representations of the first and second
matrices, and determines image displacement based on the computed
phase differences.
[0037] FIGS. 5B and 5C illustrate examples of moving a layer out of
a field of view of an imaging system. In FIG. 5B, initially an
upper layer 552 at least partially obscures a lower layer 554
relative to an imaging system 106, and then that layer is moved to
a position out of the field of view of the imaging system 106. In
this case, the upper layer 552 is moved until an air void therein
lies above the lower layer 554 with respect to the imaging system.
In FIG. 5C, initially an upper layer 562 at least partially
obscures a lower layer 564 relative to the imaging system 106, and
then that layer is moved to a position out of the field of view of
the imaging system 106. In this case, the upper layer 562 is moved
until a transparent patch 566 of material therein lies above the
lower layer 564 with respect to the imaging system. For simplicity
and clarity of presentation, multiple examples are presented herein
in which, to move a layer to a position out of the field of view of
an imaging system, that layer is translated until an outer
periphery of the layer lies outside the horizontal boundaries of a
vertical imaging column. However, as illustrated in FIGS. 5B and
5C, it is not required that an outer periphery of the layer lie
outside a horizontal boundary of a vertical imaging column for that
layer to be out of a field of view of an imaging system as that
term is used herein. Rather, by out of the field of view, it is
meant that the layer is in a position such that no obstructing
features are in the way of allowing a clean image of a different
layer to be acquired by the imaging system.
[0038] FIG. 6 illustrates alignment state sensing according to an
embodiment. At step 602, the layers are inserted into the apparatus
100 using the general positioning system 116. At step 604, the
alignment state is determined using the imaging system 106,
processor 112, memory 114, and fine positioning system 108.
Generally speaking, step 604 is detailed further in relation to
FIGS. 7-11. At step 606, the layers can be placed into a desired
alignment state by the fine positioning system 108, if
applicable.
[0039] FIG. 7 illustrates alignment state sensing according to an
embodiment. For clarity, each of FIGS. 7-11 and FIGS. 12-16
illustrate (i) method steps on the left-hand side, (ii) a
simplified, one-dimensional layer positioning representation in the
middle, and (iii) corresponding image frames, if any, on the
right-hand side. Generally speaking, a dotted-line image frame
refers to a stored image, while a solid-line image frame refers to
a "live" image that would be seen with the layers in their current
state. As illustrated herein, sometimes the "live" images are
usable, while other times they are not usable, according to the
described methods.
[0040] FIG. 7 illustrates an upper layer 752 having an alignment
marker 753 and a lower layer 754 having an alignment marker 755 in
an initial alignment state within a field of view 760 of an imaging
system having a depth of focus greater than the layer separation,
as indicated by a narrow hypothetical cone beam 758. The upper
layer 752 at least partially obscures the alignment marker 755 of
the lower layer 754, as indicated by the hash marks over the lower
layer alignment marker in the frame 780. At step 702, the upper
layer 752 is moved out of the field of view 760. At step 704, a
first image comprising at least a portion of the lower layer 754
including the alignment marker 755 is acquired and stored (S1). At
step 706, the upper layer 752 is precision-restored to its initial
position by the fine positioning system 108, and the initial
alignment state is determined using the first stored image S1 and a
second image 784, the second image 784 including the alignment mark
753 of the upper layer 752. The initial alignment state can thereby
be made directly using the positions of the alignment marks 753 and
755 relative to the imaging system, which serves as the frame of
reference. Advantageously, this process is facilitated because the
image S1 is now a clean image, without even a minor amount of
obscuration from the upper layer 752. By way of example, this can
make the choice of segmentation algorithm very simple, as even a
simple Gaussian blur and thresholding can yield the locations of
each alignment marker within the separate images S1 and 784.
Optionally, at step 708, the layers can be moved to a desired
alignment state.
[0041] FIG. 8 illustrates alignment state sensing according to an
embodiment. FIG. 8 illustrates an upper layer 852 having an
alignment marker 853 and a lower layer 854 having an alignment
marker 855 in an initial alignment state within a field of view 860
of an imaging system having a depth of focus greater than the layer
separation, as indicated by a narrow hypothetical cone beam 858. In
this example, it is the lower layer 854 that at least partially
obscures the upper layer 852. At step 802, the lower layer 854 is
moved out of the field of view 860. At step 804, a first image
comprising at least a portion of the upper layer 852 including the
alignment marker 853 is acquired and stored (S1). At step 806, the
lower layer 854 is precision-restored to its initial position by
the fine positioning system 108, and the initial alignment state is
determined according to alignment marker positions using the first
stored image S1 and a second image 884, the second image comprising
the alignment mark 855 of the lower layer 854. In still another
embodiment, where both layers at least partially obscure each
other, analogous steps to a combination of FIGS. 7 and 8 are
performed, with each layer being set aside as an image of the other
layer is acquired and stored.
[0042] FIG. 9 illustrates alignment state sensing according to an
embodiment. FIG. 9 illustrates a first layer 952 having an
alignment marker 953 and a second layer 954 having an alignment
marker 955 in an initial alignment state within a field of view 960
of an imaging system having a depth of focus less than the layer
separation, as indicated by a wide hypothetical cone beam 958. In
this example, the first layer 952 at least partially obscures the
second layer 954 even though they lie in disparate focal zones, as
illustrated by frame 982. At step 902, the first layer 952 is moved
out of the field of view 960, the imaging system focuses on the
second layer 954, and acquires an image 984 thereof. At step 904,
the first image is stored (S1). At step 906 the first layer 952 is
precision-restored to its initial position by the fine positioning
system 108, the focal plane is moved upward to the first layer 952,
and the initial alignment state is determined according to
alignment marker positions using the first stored image S1 and a
second image 988 comprising the alignment mark 953 of the first
layer 952, according to alignment marker positions. In another
embodiment, the first layer 952 lies underneath the second layer
954 relative to the imaging system, and analogous steps are
performed. In still another embodiment, where both layers at least
partially obscure each other, analogous steps are performed except
that each layer is set aside as an image of the other layer is
acquired and stored.
[0043] In the event the top layer is completely opaque, and in the
event the interesting surface of the top layer faces downward
relative to the imaging system, one effective way of resolving
alignment issues in the context of a single-camera alignment scheme
is to implement an alignment marker that goes all the way through
that layer in a through-hole manner. In this way, the need for
copying any underside surface pattern to the top surface, which can
be unreliable and introduce errors in its own right, is
avoided.
[0044] FIG. 10 illustrates alignment state sensing according to an
embodiment. FIG. 10 illustrates a first layer 1052 and a second
layer 1054 in an initial alignment state within a field of view
1060 of an imaging system having a depth of focus greater than the
layer separation, as indicated by a narrow hypothetical cone beam
1058. In this example, it is assumed the layers 1052 and 1054 are
substantially identical as viewed by the imaging system, and that
the layers 1052 and 1054 at least partially obscure each other. At
step 1002, the first layer 1052 is moved out of the field of view
1060, and the imaging system acquires a first image 1082 of the
second layer 1054. At step 1004, the first image is stored (S1). At
step 1006 the first layer 1052 is restored to its initial position
by the fine positioning system 108. At step 1008 the second layer
1054 is moved out of the field of view 1060, and the imaging system
acquires a second image 1086 of the first layer 1052. At step 1012
the second image is stored (S2). At step 1014 the initial alignment
state is determined by processing the first stored image S1 and the
second stored image S2 according to an image displacement sensing
algorithm, supra, in terms of a relative offset therebetween. This
is achievable since the layers are substantially identical. If
applicable, at step 1014 the layers are moved to a desired relative
alignment state.
[0045] FIG. 11 illustrates alignment state sensing according to an
embodiment. FIG. 11 illustrates a first layer 1152 and a second
layer 1154 in an initial alignment state within a field of view
1160 of an imaging system having a depth of focus less than the
layer separation, as indicated by a wide hypothetical cone beam
1158. As with the example of FIG. 10, it is assumed the layers 1152
and 1154 are substantially identical as viewed by the imaging
system, and that the layers 1152 and 1154 at least partially
obscure each other even though they are in different focal zones.
At step 1102, the first layer 1152 is moved out of the field of
view 1160, the imaging system focuses on the second layer 1154, and
acquires a first image 1182 thereof. At step 1104, the first image
is stored (S1). At step 1106 the first layer 1152 is restored to
its initial position by the fine positioning system 108. At step
1108 the second layer 1154 is moved out of the field of view 1160,
the imaging system focuses on the first layer 1152, and acquires a
second image 1186 thereof. At step 1110 the second image is stored
(S2). At step 1112 the initial alignment state is determined by
processing the first stored image S1 and the second stored image S2
according to an image displacement sensing algorithm, supra. If
applicable, at step 1114 the layers are moved to a desired relative
alignment state. In another embodiment in which only one of the
layers (upper or lower) at least partially obscures the other, only
a subset of the steps of FIGS. 10 and 11 are required, i.e. it is
not required that the non-obscuring layer be moved aside while the
image of the obscuring layer is acquired.
[0046] FIG. 12 illustrates determining a relative position shift
between material layers according to an embodiment. Several of the
items presented in FIG. 12 are optional and/or lie outside the
relative position shift detection process, but are presented to
provide context therefor. At step 1202, the layers are inserted
into the apparatus 100 using the general positioning system 116 and
take on an initial alignment state or configuration. At step 1204,
a first image set is acquired corresponding to the initial
alignment state. Aspects of steps 1204 and 1214 are detailed
further infra with respect to FIGS. 13-16. At step 1206, some set
of operations, if desired, is performed. At step 1208, one or more
of the layers can be entirely removed, and then at step 1210 the
removed layers, or substantially identical replacement versions
thereof, can be reinserted into a subsequent alignment state or
configuration. At step 1212 the first stored image set is retrieved
from memory. At step 1214, the relative position shift between
layers between the initial and subsequent configurations is
determined using the first stored image set and the fine
positioning system, as detailed further infra with respect to FIGS.
13-16. At step 1216, knowledge of the relative position shift can
be advantageously harnessed in a variety of ways, such as for
restoring the initial alignment state, placing into a desired
alignment state relative to the initial/subsequent alignment
states, etc.
[0047] FIG. 13 illustrates determining a relative position shift
between material layers according to an embodiment. FIG. 13
illustrates a first layer 1352 having an alignment marker 1353 and
a second layer 1354 having an alignment marker 1355 in an initial
alignment state within a field of view 1360 of an imaging system
having a depth of focus less than the layer separation, as
indicated by a wide hypothetical cone beam 1358. At step 1302, in
an initial alignment state, the imaging system focuses on the first
layer 1352, and acquires and stores a first image S1-A. At step
1304, in the initial alignment state, the imaging system focuses on
the second layer 1354, and acquires and stores a second image S2-A.
As discussed previously with respect to FIG. 12, at this time
intermediate processing can occur, as represented by steps 1306
1308, causing the layers to assume a subsequent configuration.
Elements 1352' and 1354' are used to denote the first and second
layers in the subsequent alignment state, as they may optionally be
replaced by identical versions thereof during steps 1306-1308. At
step 1310, in the subsequent alignment state, the imaging system
focuses on the first layer 1352', and acquires and stores a third
image S1-B. At step 1312, in the subsequent alignment state, the
imaging system focuses on the second layer 1354, and acquires and
stores a fourth image S2-B. At step 1314, the first and third
images S1-A and S1-B are processed according to an image
displacement sensing algorithm, supra, to determine a position
shift vector V1 representing a change in the position of the first
layer 1352/1352' between the initial and subsequent configurations.
Also, the second and fourth images S2-A and S2-B are processed
similarly to determine a position shift vector V2 representing a
change in the position of the second layer 1354/1354' between the
initial and subsequent configurations. At step 1316, a relative
position shift vector VR is computed by vector subtraction of the
position shift vectors V1 and V2.
[0048] FIG. 14 illustrates determining a relative position shift
between material layers according to an embodiment. FIG. 14
illustrates a first layer 1452 having an alignment marker 1453 and
a second layer 1454 having an alignment marker 1455 in an initial
alignment state within a field of view 1460 of an imaging system
having a depth of focus less than the layer separation, as
indicated by a wide hypothetical cone beam 1458. In this example,
the first layer 1452 at least partially obscures the second layer
1454 even though they lie in disparate focal zones. At step 1402,
in an initial alignment state, the imaging system focuses on the
first layer 1452, and acquires and stores a first image S1-A. At
step 1404, the first layer 1452 is moved out of the field of view
1460, the imaging system focuses on the second layer 1454, and
acquires and stores a second image S2-A. At step 1406, the first
layer 1452 is restored to its previous position. Intermediate
processing/shuffling occurs at steps 1408-1410 similar to steps
1306-1308, supra. At step 1412, in the subsequent alignment state,
the imaging system focuses on the first layer 1452', and acquires
and stores a third image S1-B. At step 1414, the first layer 1452'
is moved out of the field of view 1460, the imaging system focuses
on the second layer 1454', and acquires and stores a fourth image
S2-B. Steps 1418-1420 proceed in a manner similar to steps
1314-1316 of FIG. 13 for determining the relative position shift
VR. As indicated by the examples of FIGS. 13-14, while the image
displacement sensing algorithm is indeed effective when alignment
markers are present, the alignment markers themselves are only
"used" in the sense that they represent some type of surface
texture for the layers. In another embodiment, the first layer 1452
lies underneath the second layer 1454 relative to the imaging
system, and analogous steps are performed. In still another
embodiment, where both layers at least partially obscure each
other, analogous steps are performed except that each layer is set
aside as the an image of the other layer is acquired and
stored.
[0049] FIG. 15 illustrates determining a relative position shift
between material layers according to an embodiment. FIG. 15
illustrates a first layer 1552 and a second layer 1554 in an
initial alignment state within a field of view 1560 of an imaging
system having a depth of focus less than the layer separation, as
indicated by a wide hypothetical cone beam 1558. Here, the layers
do not have alignment markers, but do possess surface textures
sufficient for an image displacement sensing algorithm, supra. At
step 1502, in an initial alignment state, the imaging system
focuses on the first layer 1552, and acquires and stores a first
image S1-A. At step 1504, in the initial alignment state, the
imaging system focuses on the second layer 1554, and acquires and
stores a second image S2-A. Intermediate processing/shuffling
occurs at steps 1506-1508 as discussed for steps 1306-1308, supra.
At step 1510, in the subsequent alignment state, the imaging system
focuses on the first layer 1552', and acquires and stores a third
image S1-B. At step 1512, in the subsequent alignment state, the
imaging system focuses on the second layer 1554, and acquires and
stores a fourth image S2-B. Steps 1516-1518 proceed in a manner
similar to steps 1314-1316 of FIG. 13 for determining the relative
position shift VR.
[0050] FIG. 16 illustrates determining a relative position shift
between material layers according to an embodiment. FIG. 16
illustrates a first layer 1652 and a second layer 1654 in an
initial alignment state within a field of view 1660 of an imaging
system having a depth of focus less than the layer separation, as
indicated by a wide hypothetical cone beam 1658. In this example,
the layers at least partially obscure each other even though they
lie in disparate focal zones. At step 1602, in an initial alignment
state, the second layer 1654 is moved out of the field of view, and
the imaging system focuses on the first layer 1652 and acquires and
stores a first image S1-A. At step 1604, the position of the second
layer 1654 is restored, the first layer 1652 is moved out of the
field of view, and the imaging system focuses on the second layer
1654 and acquires and stores a second image S2-A. Intermediate
processing/shuffling occurs at steps 1608-1608 similar to steps
1306-1308, supra. At step 1610, in the subsequent alignment state,
the second layer 1654 is moved out of the field of view, and the
imaging system focuses on the first layer 1652 and acquires and
stores a third image S1-B. At step 1612, the position of the second
layer 1654 is restored, the first layer 1652 is moved out of the
field of view, and the imaging system focuses on the second layer
1654 and acquires and stores a fourth image S2-B. At step 1614, the
position of the first layer 1652 is restored. Steps 1616-1618
proceed in a manner similar to steps 1314-1316 of FIG. 13 for
determining the relative position shift VR. In other embodiments in
which only a first layer partially obscures a second layer, the
second layer not obscuring the first layer, an analogous subset of
the steps of FIG. 16 are performed, and can be used where the
obscuring layer lies above or below the obscured layer.
[0051] FIG. 17 illustrates alignment sensing according to an
embodiment. FIG. 17 illustrates a first layer 1752 and a second
layer 1754 in an initial alignment state within a field of view
1760 of an imaging system having a depth of focus less than the
layer separation, as indicated by a wide hypothetical cone beam
1758. As with the example of FIGS. 10-11, supra, it is assumed the
layers 1752 and 1754 are substantially identical as viewed by the
imaging system. At step 1702, the imaging system focuses on the
first layer 1752, and acquires a first image 1780 thereof. At step
1704, the first image is stored (S1). At step 1706 the imaging
system focuses on the second layer 1154, and acquires a second
image 1782 thereof. At step 1708 a relative offset between the
first layer 1752 and the second layer 1754 is determined by
processing the first stored image S1 and the second image 1782
according to an image displacement sensing algorithm, supra. If
applicable, at step 1710 the layers are moved to a desired relative
offset.
[0052] FIG. 18 illustrates determining a relative position shift
between material layers according to an embodiment. FIG. 18
illustrates a first layer 1852 and a second layer 1854 in an
initial alignment state within a field of view 1860 of an imaging
system having a depth of focus greater than the layer separation,
as indicated by a narrow hypothetical cone beam 1858. The layers at
least partially obscure each other. At step 1802, in an initial
alignment state, the second layer 1854 is moved out of the field of
view, and the imaging system acquires and stores a first image S1-A
of the first layer 1852. At step 1804, the position of the second
layer 1854 is restored, the first layer 1852 is moved out of the
field of view, and the imaging system acquires and stores a second
image S2-A of the second layer 1854. Intermediate
processing/shuffling occurs at steps 1808-1808 similar to steps
1306-1308, supra. At step 1810, in the subsequent alignment state,
the second layer 1854 is moved out of the field of view, and the
imaging system acquires and stores a third image S1-B of the first
layer 1852. At step 1812, the position of the second layer 1854 is
restored, the first layer 1852 is moved out of the field of view,
and the imaging system acquires and stores a fourth image S2-B of
the second layer 1854. At step 1814, the position of the first
layer 1852 is restored. Steps 1816-1818 proceed in a manner similar
to steps 1314-1316 of FIG. 13 for determining the relative position
shift VR. In other embodiments in which only a first layer
partially obscures a second layer, the second layer not obscuring
the first layer, an analogous subset of the steps of FIG. 18 are
performed, and can be used where the obscuring layer lies above or
below the obscured layer.
[0053] It is to be appreciated that embodiments involving more than
three layers are also within the scope of the present teachings. It
is to be further appreciated that the present teachings are widely
applicable in a variety of physical circumstances in which at least
one of alignment sensing and control is desired. Examples include
contact lithography, proximity lithography, nanoimprint
lithography, or any of a variety of other processes relating to the
fabrication or use of very small devices
[0054] Whereas many alterations and modifications of the
embodiments will no doubt become apparent to a person of ordinary
skill in the art after having read the foregoing description, it is
to be understood that the particular embodiments shown and
described by way of illustration are in no way intended to be
considered limiting. By way of example, image displacement sensing
algorithm can refer to any of a variety of different image flow
algorithms adapted for the rigid body assumption including, but not
limited to, differential methods, tensor methods, correlation
methods, phase methods, and error analysis methods. By way of
further example, many combinations of the described embodiments are
also within the scope of the present teachings, such as having a
first layer without alignment markers whose first position shift is
sensed using an image displacement sensing algorithm, and a second
layer with an alignment marker whose second position shift is
sensed according to alignment marker displacement, wherein the
overall relative position shift is computed by vector subtraction
of the first and second position shifts. Thus, reference to the
details of the described embodiments are not intended to limit
their scope.
* * * * *